A new book claims that singer and actor Frank Sinatra always believed that Marilyn Monroe was murdered.

Monroe was found dead from an accidental overdose in August 1962, but it is alleged that Sinatra believed her death was associated with her high-profile affairs with John F Kennedy and his brother, Robert.

In the memoir titled Sinatra and Me: In The Wee Small Hours, Tony Oppedisano, Sinatra’s former manager and close friend, writes: “Frank believed she was murdered, and he never got over it.”

The book claims that Monroe, the star of films including Some Like It Hot and The Misfits, often confided in Sinatra, with whom she was close.

After her affairs with the Kennedy brothers ended, and she was ostracised by them, Monroe allegedly told Sinatra “she didn’t understand why they’d shut her out completely once she stopped having sex with them”.

The book claims that shortly before her death, Monroe was staying at the Cal Neva Lodge near Lake Tahoe – which Sinatra part-owned – with her ex-husband, the baseball star Joe DiMaggio.

While there, a press conference was announced that Monroe was due to be present at, but she died before it could take place.

The book claims the actor was set to announce her reunion with DiMaggio.

However, many believed she would share secrets about her affairs with the Kennedys, and the book claims that Sinatra thought she was silenced because of this assumption.

Oppedisano writes: “Frank believed if the press conference hadn’t been announced, she would have lived a lot longer.”

It is also claimed that Sinatra “never” thought she’d share secrets of the affairs as she “still had feelings” for John.

The book alleges that several sources told Sinatra that “she’d been murdered with a Nembutal suppository” and that “Robert Kennedy or the mob was involved”.

Nembutal is a powerful sedative that can be administered as a suppository, pill or injection, and can be fatal in large doses.

Monroe was 36 at the time of her death, and Sinatra died from a heart attack in 1998, aged 82.

The allegations in the book are not new; the theory that Monroe was murdered has been circulating for decades.

There have been numerous investigations and conspiracy theories about her death, including claims that she was killed by the Kennedys or by the mafia.

However, no concrete evidence has ever been found to support these claims.

Monroe’s death was officially ruled as a probable suicide due to an overdose of barbiturates.

The actress had a history of depression and substance abuse, and had attempted suicide several times in the past.

She was also reportedly unhappy with the direction of her career and had recently been fired from the film Something’s Got to Give.

Monroe’s death shocked the world and she has since become an icon of popular culture.

Her legacy has been celebrated in countless books, films and songs, and her image continues to captivate audiences around the world.

The actress’s relationship with the Kennedys, in particular, has been the subject of much fascination and speculation, with many historians and biographers attempting to uncover the truth behind the rumours and allegations.

Sinatra’s belief that Monroe was murdered is not surprising, given his close relationship with the actress.

The two stars were rumored to have had a romantic relationship, although the exact nature of their relationship remains unclear.

Sinatra was also known to be friends with the Kennedy family and was a strong supporter of John F Kennedy’s presidential campaign.

In the years since Monroe’s death, many people have come forward with their own theories about what really happened.

Some have claimed that the actress was killed by the Kennedys, who were concerned about the potential fallout from their relationship.

Others have suggested that the mafia was involved, possibly as a result of Monroe’s connections to organized crime figures.

Despite the many investigations and conspiracy theories, the truth about Monroe’s death may never be fully known.

The actress’s life and legacy continue to fascinate and intrigue people around the world, and her untimely death remains one of Hollywood’s greatest mysteries.

The publication of this new book is likely to reignite interest in Monroe’s death and the various theories surrounding it.

While some may see Sinatra’s belief that she was murdered as further evidence of foul play, others may view it as nothing more than a celebrity rumor.

Regardless of what one believes about Monroe’s death, there is no denying the enduring legacy of the actress and the impact she had on popular culture.

From her iconic performances to her glamorous image and tragic end, Marilyn Monroe remains one of the most enduring and enigmatic figures in Hollywood history.